The hydroformylation reaction, also known as the oxo reaction, is used extensively in commercial processes for the preparation of aldehydes by the reaction of one mole of an olefin with one mole each of hydrogen and carbon monoxide. A particularly important use of the reaction is in the preparation of normal (n-) and butyraldehyde(iso-) from propylene. Both products are key building blocks for the synthesis of many chemical intermediates like alcohols, carboxylic acids, esters, plasticizers, glycols, essential amino acids, flavorings, fragrances, polymers, insecticides, hydraulic fluids, and lubricants.
At present, high n-selectivity is more easily achieved whereas achievement of high iso-selectivity remains challenging. Different approaches have been attempted throughout the years to tackle this problem, including the use of various ligands (Phillips, Devon, Puckette, Stavinoha, Vanderbilt, (Eastman Kodak Company), U.S. Pat. No. 4,760,194) and carrying out reactions under aqueous conditions (Riisager, Eriksen, Hjorkjær, Fehrmann, J. Mol. Catal. A: Chem. 2003, 193, 259). The results have generally not been satisfactory, with either unimpressive iso-selectivity and/or because the reaction needs to be run at an undesirable temperature. The highest iso-selectivity reported was 63% in a reaction carried out at 19° C. (Norman, Reek, Besset, (Eastman Chemical Company), U.S. Pat. No. 8,710,275). However, in some instances this is not desirable because hydroformylation reactions conducted at lower temperatures may result in lower reaction rates, so carrying out the reaction at a higher temperature is generally preferred in industry. In this case, the iso-selectivity was reduced to 38% when the reaction was carried out at 80° C. Thus, there remains a need for catalysts with high iso-selectivity at temperatures above 19° C.